Speaker cabinet with tuned stress elements

ABSTRACT

A speaker cabinet has front and back walls and side walls defining a sound chamber, and a location for supporting at least one speaker in one of the walls. Thin metallic stress elements extend between and are connected to selected pairs of walls, and are loaded undertensile stress so as to tune them to desired resonant frequencies. The tuned stress elements vibrate in response to excitation by sound waves emitted from the speaker, thus producing additional sound which enhances the sound from the speaker. Tensioning means provide for selectively adjusting the tensile stress and resonant frequencies of the stress elements and, consequently, the character of the sound produced by vibration of the stress elements.

[0001] This application is a continuation-in-part of U.S. patent application No. 09/545,951, filed on Apr. 10, 2000.

FIELD OF THE INVENTION

[0002] The invention relates to speaker cabinets for use with audio speakers, and in particular to speaker cabinets having internal stress elements tuned to desired resonant frequencies.

BACKGROUND OF THE INVENTION

[0003] Audio speakers are conventionally mounted in boxes known as speaker cabinets. Usually the cabinets are rectangular boxes with front and back panels and side panels and top and bottom panels, and are made of wood or wood composition board material, although other materials have been known in some cases.

[0004] The speakers are usually mounted in a front wall or panel of the cabinet. Audio frequency sound waves from the speakers are propagated both forwardly and rearwardly of the speaker cone of each speaker. The sound waves propagating forwardly of the speakers simply propagate out into the room or space in which the cabinet is located.

[0005] However, the sound waves propagated rearwardly of the speaker are caught within the interior of the cabinet. It is well known, although not entirely understood, that the size and shape of the cabinet, and the material of the cabinet walls or panels, will have a significant effect on the overall quality of the sound which is heard by listeners. Usually the cabinet panels are made of relatively thick heavy material such as wooden particle board, in the hope that this will somehow improve the quality of the sound reproduction. Apparently, it is believed, the thicker and stiffer the panels, the better will be the sound quality. In practice, however, even heavy cabinets made of costly materials do not always result in improved quality sound. Varying the dimensions of the cabinet is also believed to have an effect on the quality of the sound, but in spite of various different makers producing cabinets of widely differing shapes and sizes and materials, a significant improvement in sound quality has not been achieved. It appears that the action of the sound waves within the cabinet is still not totally understood. The clear quality of sound which should be achieved in theory is not reached in practice.

[0006] The speaker cabinet construction is now believed to create random noise or distortion due, at least in part, to the propagation of the sound waves from the rear of the speaker which are trapped within the cabinet. Apparently, the problem is at least partly due to the fact that the propagation of the sound waves within the cabinet sets up random noise signals which, when heard in combination with the original sound signal, cause unpleasant sounds which interfere with the enjoyment of the original sound. The low frequency noise generated by the feedback of the sound waves within the cabinet is regarded as relatively powerful and destructive. The low frequency sounds from the speaker may be propagated forwardly through a speaker cabinet port to reduce the pressure from inside the cabinet generated by the low frequency of sound from the back of the speaker.

[0007] However, the random noise signals in the mid-ranges and high frequency ranges generated within the speaker cabinet are regarded as undesirable. Accordingly, it has been the practice in the past to incorporate sound damping materials within the cabinet. These materials may include, for example, thermal insulation material which have sound absorption or sound damping capabilities. The intent is to absorb and hide the higher and mid-range frequency random noise signals.

[0008] This practice has led to a reduction in the overall volume and feedback of the higher and mid-range frequencies, whereas the low range frequency sounds have remained at a higher volume. Clearly this is undesirable and, if possible, should be avoided.

[0009] The adjustment of the speakers within the cabinet to separate high, medium and low frequencies, and the distortion of original sound, is usually controlled by electronic cross-over circuitry and amplification of the speakers. Moreover, the process of adjusting the tones and sound waves within the cabinet has been attempted in the industry through electronics.

[0010] The prior art discloses numerous attempts to improve the quality of sound produced by conventional speakers mounted in speaker cabinets. A comparatively early attempt is found in U.S. Pat. No. 2,840,181 issued on Jun. 24, 1958 to Wildman, which describes a rectangular cabinet having a circular aperture in its front wall, a triangular aperture in its back wall, and a baffle extending between the top and bottom panels of the cabinet. The baffle is provided to alter the quality of sound produced by the speaker cabinet by virtue of the fact that there is no direct path for sound to travel between the front aperture and the rear aperture. The Wildman cabinet also features a number of struts extending between the front and rear walls (and passing through the baffle), and a number of rods extending between the side walls. The struts and rods are provided to prevent movement of the walls relative to each other, such movement being believed to have an undesirable effect on the operation of the speaker cabinet. These struts and rods are preferably glued in place where they connect to their corresponding walls; they are not stressed in any manner, and no means is provided for loading them under any kind or stress.

[0011] U.S. Pat. No. 5,661,271 issued on Aug. 26, 1997 to Moser describes a rectangular speaker cabinet of laminated construction. The cabinet is made up of a number of horizontal structural laminations each of which may have an opening or openings of a desired size such that when the laminations are clamped together, padlock-style, the openings in the laminations define a substantially spherical sound chamber or chambers, which shape is believed to have an effect on the quality of sound produced by the speaker cabinet. There are no secondary elements extending into or passing through the sound chamber or chambers of the Moser cabinet; tensioned bolts, running vertically, are used to clamp the structural laminations of the cabinet together, but these bolts pass entirely through the solid material of the structural laminations and do not impinge on the sound chamber.

[0012] The foregoing examples of the prior art disclose speaker cabinets that have fixed and non-variable characteristics, and thus are not amenable to any kind of adjustment which might have beneficial effects on the quality of sound being produced. Accordingly, it is desirable to provide speaker cabinets which are capable of delivering crisp, clear, distortion-free sound, and which also have means for “tuning” the cabinets mechanically so that the quality of sound produced by the speaker cabinet may be altered and enhanced as the listener may desire.

BRIEF SUMMARY OF THE INVENTION

[0013] With a view to providing a speaker cabinet which goes some way towards achieving these results, the invention in one aspect is a speaker cabinet having:

[0014] (a) a top panel and a bottom panel, and a plurality of walls disposed between and connecting to the top panel and bottom panel, said top panel, bottom panel, and walls defining a sound chamber;

[0015] (b) means for supporting a speaker in one of the walls; and

[0016] (c) one or more elongate stress elements passing through the sound chamber and extending between two of the walls, each stress element having a first end and a second end;

[0017] wherein:

[0018] (d) the first and second ends of each stress element are connected, respectively, to the walls between which the stress element extends; and

[0019] (e) each stress element is loaded under longitudinal tensile stress.

[0020] In the preferred embodiment, the walls include a front wall and a back wall, plus two side walls each disposed between and at substantially right angles to said front wall and back wall. As well, the speaker support means is located in the front wall, and one or more stress elements extend between the front wall and the back wall. One or more additional stress elements may extend between the front wall and the back wall.

[0021] The stress elements are preferably disposed substantially parallel to each other and substantially normal to the wall between which they extend.

[0022] In the preferred embodiment, the walls are planar. However, in alternative embodiments, one or more of the walls may be curvilinear. In fact, the walls may comprise a number of curvilinear sections which are joined together without sharp demarcation, such that the cabinet takes a substantially cylindrical shape.

[0023] In the preferred embodiment, the stress elements are made substantially of metal. Most preferably, the stress elements are made of steel or copper. The stress elements may be thin rods or wires, of substantially circular cross-section. Alternatively, the stress elements may be cables or wound metal strings, similar to bass strings of guitars or pianos.

[0024] In the preferred embodiment, the speaker cabinet includes tensioning means for varying the tensile stress in each stress element. Such tensioning means may be provided by threading one of each stress element is threaded, and providing a threaded sleeve engageable with the threads of the stress element. The sleeve is rotatably mounted in the wall corresponding to the threaded end of the stress element, and the sleeve also has tool-engagement means whereby the sleeve may be rotated relative to the stress element.

[0025] Also in the preferred embodiment, each stress element is tensioned such that its resonant frequency is in the range between about 200 cycles per second and 600 cycles per second; i.e., between about 200 Hertz (Hz) and about 600 Hz.

[0026] The speaker cabinet may be conveniently fabricated from ordinary lumber or wood particle board. However, other materials, such as thermoplastics, may be used as well.

[0027] In another aspect, the invention is a speaker cabinet having:

[0028] (a) a top panel and a bottom panel, a front wall and a back wall, plus two side walls each disposed between and at substantially right angles to said front wall and back wall, wherein:

[0029] (i) the front wall, back wall, and side walls are disposed between and are connected to said top panel and bottom panel;

[0030] (ii) the top panel, bottom panel, front wall, back wall, and side walls define a sound chamber; and

[0031] (iii) the front wall defines an opening for a speaker, and includes means for supporting said speaker therein;

[0032] (b) a first plurality of elongate metallic stress elements passing through the sound chamber and extending between the front wall and the back wall; and

[0033] (c) tensioning means comprising, for each stress element, a threaded sleeve engageable with the threads of the stress element, said sleeve being rotatably mounted in the wall corresponding to the threaded end of the stress element, said sleeve also having tool-engagement means whereby the sleeve may be rotated relative to the stress element;

[0034] wherein:

[0035] (d) the first and second ends of each stress element are connected, respectively, to the front, rear, or side walls between which the stress element extends;

[0036] (e) the stress elements are substantially parallel to each other and substantially normal to the front wall and the back wall; and

[0037] each stress element is loaded under longitudinal tensile stress such that its resonant frequency is in the range between about 200 Hz and about 600 Hz.

[0038] The various features of novelty which characterize the invention are pointed out with more particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention.

IN THE DRAWINGS

[0039]FIG. 1 is a perspective on a typical speaker cabinet partially cut away to reveal its construction, illustrating the stress elements in one embodiment.

[0040]FIG. 2 is a section along line 2-2 of FIG. 1.

[0041]FIG. 3 is a section along line 3-3 of FIG. 1.

[0042]FIG. 4 is an enlarged side elevation of both ends of a typical stress element.

DESCRIPTION OF A SPECIFIC EMBODIMENT

[0043] Referring to FIG. 1, it will be seen that this preferred embodiment of the invention is illustrated, in this case, in the form of a speaker cabinet indicated generally by reference numeral 10. Cabinet 10 is a typical rectangular box comprising a front wall 12, a rear wall 14, side walls 16, a top wall 18, and a bottom wall (not shown), all of which define and enclose an interior sound chamber 19. Although the cabinet 10 in this embodiment has only fourwalls, all of which are planar, in other embodiments the cabinet 10 may have a different number of walls, or one or more of the walls could be curvilinear, without departing from the essential principles of the invention. Typically the walls of the cabinet are made of, for example, wooden particle board. Other materials such as injection molded thermoplastic materials may also be used.

[0044] In the preferred embodiment, front wall 12 is provided with speaker mounting locations in the form of opening 20 for a bass speaker, opening 22 for a mid-range speaker, and opening 24 for a high-range speaker. Conventional speakers, namely bass speaker 26, mid-range speaker 28, and high frequency speaker 30 are mounted on front wall 12 in registration with their respective openings.

[0045] The number of speakers depends on the design of the system. A cabinet may have only one speaker or two speakers, and may have more than three speakers in some cases.

[0046] The speakers are connected through suitable cross-over circuits of a type well known in the art, and are connectable to a source of audio signals. The signal source is not relevant to the invention and is omitted from the drawings for the sake of clarity. The cross-over circuits (not shown) divide the signals from the signal source into bass, mid-range, and high-range signals, and connect the divided signals to their respective speakers. All of this is well known in the speaker art and requires no special description. In the case of single speaker systems, all the audio signals are fed to the single speaker. Although not shown, the cabinet may feature one or more “ports” of a type well known in the art, for propagating sounds forwardly from within the cabinet. These ports are openings extending from through the speaker cabinet wall or walls, providing a pathway for sound to travel directly from the sound chamber out into the room or space in which the speaker cabinet is situated. The configuration, location, and dimensions of such ports may be selectively determined as appropriate to achieve desired effects.

[0047] Also, as is well known, the speakers are almost always of the moving cone type. As signals pass through the speaker coils the cones vibrate and sound waves are propagated both forwardly and rearwardly of the speaker cones.

[0048] The sound waves moving forwardly in the speakers are propagated within the room and produce audible sound with whatever degree of clarity is possible from those speakers. However, it has been found that the sound waves propagated rearwardly of the speakers do not reproduce clear audible sound, but instead generate unwanted audible noise which appears to distort the true sound quality which is desired.

[0049] In order to combat this there is provided, in accordance with the invention, a form of speaker cabinet tuning means in which stress elements are connected between walls of the cabinet, and are tensioned to a predetermined tension. The precise effect of the stress elements is not as yet totally explained, but is believed to be essentially as described herein. Whatever the precise working of the stress elements may be, it has been observed that a cabinet with the addition of the stress elements will develop a far clearer high quality sound than a cabinet without them.

[0050] By way of illustration, FIGS. 1, 2 and 3 show the speaker cabinet 10 having one or more stress elements 32. The stress elements 32 extend from the front wall 12 to the rear wall 14 within the interior of the cabinet 10. The stress elements 32 are loaded longitudinally under tensile stress, and as is readily apparent from the Figures, they pass through the sound chamber 19 for the major portion of their length. Accordingly, the stress elements 32 are directly exposed to and may be excited by sound waves emanating from a speaker mounted in the cabinet 10. This excitation of the stress elements 32 induces vibration in the stress elements 32, and that vibration produces sound, in a way directly analogous to the well-known way that sound is produced by inducing vibration in the strings of a violin, a piano, or a guitar. The sound thus produced is a mechanically-produced sound that is qualitatively different from sounds which are electronically produced or enhanced by the speakers. Such mechanically-produced sound is considered by many to be richer, more natural, and therefore more pleasurable to the ear than sound which is electronically produced or enhanced.

[0051] In accordance with the invention, the resonant frequency of stress elements 32 may be selectively adjusted by varying the level of tensile stress in stress elements 32, just as strings of musical instruments may be tuned by adjusting the tension therein. As is well known in the art, the pitch and quality of sound produced from a vibrating element such as a piano string will vary according to the resonant frequency to which it is tuned. Therefore, the characteristics of the sound produced by stress elements 32 of the present invention, as well as the overall quality of the sound produced by speaker 10 of the invention, may be adjusted, as a listener may prefer, by adjusting the tension in stress elements 32. Moreover, the sound produced from speaker cabinet 10 is found to be of quality different from electronically-produced sound which would be produced by the speakers alone, apparently because it is enhanced by mechanically-produced sound from the vibrating stress elements 32.

[0052] The stress elements 32, in the preferred embodiment, are thin rods of metal, preferably steel. However, in some cases they may be steel cables, and it is possible that strings from stringed musical instruments will function in the same way. In an alternative embodiment, the stress elements 32 may be fashioned from copper.

[0053] Preferably in a three-speaker cabinet there will be several stress elements 32 spaced about over the area of at least two walls. The stress elements 32 preferably are disposed substantially parallel to one another, and substantially normal to the planes of the two walls (in the case where the two walls are parallel to each other). There may also be further elements 32 extending between opposite side walls 16 (phantom lines in FIG. 3).

[0054] In the illustrated embodiment, there are eight stress elements 32 parallel with one another and normal to the planes of the front and rear walls. FIG. 1 also shows six transverse stress elements 32 between side walls 16. However, quantities and orientations of stress elements 32 different from those described herein may be used without departing from the intended scope of the invention.

[0055] Tensioning of the stress elements 32 is achieved in the preferred embodiment by the means shown in FIG. 4, which illustrates the ends of one stress element 32. It will be seen that one end (32A) is threaded as at 34. A socket 36 is provided having internal threads. Socket 36 has a head 38 with a torque device, in this case a slot 40 extending thereacross. In this embodiment there is one such socket 36 for each stress element 32, at one end. Each stress element 32 is provided at the other end 32B with a fixed plug 42 secured thereto by any suitable means.

[0056] Each of front and rear walls 12 and 14 (and side walls 16, if transverse stress elements are used) is drilled with small openings 44 and 46 registering with one another. Plugs 42 are received in openings 44. The openings 46 are sized so as to receive sockets 36 therein, but their heads 38 are too large to pass through the openings 46, and therefore retain the sockets 36 in their openings 46. The threaded ends 34 of stress elements 32 are introduced into their corresponding threaded sockets 36, and the sockets 36 are then rotated by a suitable tool engaging their respective slots 40. In this way, the stress elements 32 may be tensioned to desired tension levels and resonant frequencies.

[0057] The tensile forces thus induced in stress elements 32 will be naturally transferred to the walls in which the stress elements 32 are mounted, thereby biasing the walls toward each other. As mentioned previously, the walls may be fabricated from any of several materials, but the type of material used is not critical to the present invention. It is only important that the walls be strong enough to withstand the tensile forces transferred to them from the stress elements 32, without buckling or deflecting to such extent that the tensile stresses in the stress elements 32 are substantially relieved.

[0058] It will be readily apparent to those skilled in the art that other means of tensioning stress elements 32 may be used without departing from the essential concept of the present invention.

[0059] The stress elements 32 preferably will be tensioned so as to vibrate at a frequency of between 200 Hz and 600 Hz. Experiments have shown that when the stress elements 32 are tensioned to a frequency is this range, the speaker cabinet 10 will demonstrate a marked improvement in quality and clarity of sound reproduction. However, in alternative embodiments the stress elements 32 may be tuned to frequencies outside this range.

[0060] The foregoing is a description of a preferred embodiment of the invention which is given here by way of example only, and the invention is not to be taken as limited to any of the specific features described. It will be readily seen by those skilled in the art that various modifications of the present invention may be devised without departing from the essential concept of the invention, and all such modifications are intended to be included in the scope of the claims appended hereto. 

What is claimed is:
 1. A speaker cabinet having: (a) a top panel and a bottom panel, and a plurality of walls disposed between and connecting to the top panel and bottom panel, said top panel, bottom panel, and walls defining a sound chamber; (b) means for supporting a speaker in one of the walls; and (c) one or more elongate stress elements passing through the sound chamber and extending between two of the walls, each stress element having a first end and a second end; wherein: (d) the first and second ends of each stress element are connected, respectively, to the walls between which the stress element extends; and (e) each stress element is loaded under longitudinal tensile stress.
 2. The speaker cabinet of claim 1, wherein the walls include a front wall and a back wall, plus two side walls each disposed between and at substantially right angles to said front wall and back wall.
 3. The speaker cabinet of claim 2, wherein the speaker support means is located in the front wall, and in which one or more stress elements extend between the front wall and the back wall.
 4. The speaker cabinet of claim 3, wherein the one or more stress elements extend between the front wall and the back wall.
 5. The speaker cabinet of claim 4, wherein the stress elements are disposed substantially parallel to each other and substantially normal to the front wall and the back wall.
 6. The speaker cabinet of claim 4, further having one or more stress elements extending between the side walls.
 7. The speaker cabinet of claim 6, wherein the stress elements extending between the side walls are disposed substantially parallel to each other and substantially normal to the side walls.
 8. The speaker cabinet of claim 1, wherein at least one of the walls is curvilinear.
 9. The speaker cabinet of claim 1, wherein the stress elements are made substantially of metal.
 10. The speaker cabinet of claim 9, wherein the stress elements are made substantially of a metal selected from the group consisting of steel and copper.
 11. The speaker cabinet of claim 1, wherein one wall defines one or more ports.
 12. The speaker cabinet of claim 1, further comprising tensioning means for varying the tensile stress in each stress element.
 13. The speaker cabinet of claim 12, wherein one end of each stress element is threaded, and wherein the tensioning means comprises a threaded sleeve engageable with the threads of the stress element, said sleeve being rotatably mounted in the wall corresponding to the threaded end of the stress element, said sleeve also having tool-engagement means whereby the sleeve may be rotated relative to the stress element.
 14. The speaker cabinet of claim 1, wherein each stress element is tensioned such that its resonant frequency is in the range between about 200 Hz and about 600 Hz.
 15. The speaker cabinet of claim 1, wherein at least one wall is fabricated from a material selected from the group consisting of lumber and wood particle board.
 16. The speaker cabinet of claim 1, wherein at least one wall is fabricated from a thermoplastic material.
 17. A speaker cabinet having: (a) a top panel and a bottom panel, a front wall and a back wall, plus two side walls each disposed between and at substantially right angles to said front wall and back wall, wherein: (i) the front wall, back wall, and side walls are disposed between and are connected to said top panel and bottom panel; (ii) the top panel, bottom panel, front wall, back wall, and side walls define a sound chamber; and (iii) the front wall defines an opening for a speaker, and includes means for supporting said speaker therein; (b) a first plurality of elongate metallic stress elements passing through the sound chamber and extending between the frontwall and the back wall; and (c) tensioning means comprising, for each stress element, a threaded sleeve engageable with the threads of the stress element, said sleeve being rotatably mounted in the wall corresponding to the threaded end of the stress element, said sleeve also having tool-engagement means whereby the sleeve may be rotated relative to the stress element; wherein: (d) the first and second ends of each stress element are connected, respectively, to the front, rear, or side walls between which the stress element extends; (e) the stress elements are substantially parallel to each other and substantially normal to the front wall and the back wall; and (f) each stress element is loaded under longitudinal tensile stress such that its resonant frequency is in the range between about 200 Hz and about 600 Hz.
 18. The speaker cabinet of claim 17, further comprising a second plurality of elongate stress elements passing through the sound chamber and extending between the side walls, each stress element having a first end and a threaded second end, and wherein the second plurality of stress elements are substantially parallel to each other and substantially normal to the side walls.
 19. The speaker cabinet of claim 17, wherein the stress elements are made substantially of a metal selected from the group consisting of steel and copper.
 20. The speaker cabinet of claim 17, wherein at least one wall is fabricated from a material selected from the group consisting of lumber and wood particle board, and wherein one wall defines one or more ports. 